SPACE PROVIDED. Many key processes are regulated by tyrosyl phosphorylation, which is controlled by protein-tyrosine kinases (PTKs) and protein-tyrosine phosphatases (PTPs). Abnormal regulation of such pathways can lead to developmental defects and diseases such as cancer. Understanding cellular regulation requires defining the relevant PTKs and PTPs and their interactions. This in turn may lead to new, more selective drugs for human disease. The goal of our research is to understand the biological function, mechanism of action, and role in disease of the PTPs Shp2 and PTPIB. Shp2, encoded by PTPN11, is required for vertebrate development and is a positive (signal-enhancing) component in growth factor, cytokine and integrin signaling. Autosomal dominant PTPN11 mutations cause half of Noonan syndrome (NS) and nearly all LEOPARD syndrome (LS). NS and LS are neurocardiofacial cutaneous' (NCFC) syndromes, other examples of which include cardiofacial cutaneous syndrome (CFC), caused by BRAF or MEKl/2 mutations, and Costello Syndrome, caused by HRAS mutations. Most ofthe genes that cause NCFC syndromes are oncogenes, and most NCFC associated with cancer predisposition; Notably, somatic PTPN11 mutations contribute to leukemias. During the initial years of this MERIT award, we characterized the properties of NS-associated Shp2 mutants and also found that, in contrast to the prevailing view, LS mutants are catalytically impaired, dominant negative alleles. We established the first mouse models for NS, delineated a key pathway by which Shp2 controls Ras activation, and identified the Ras exchange factor, SOSl as another major NS gene. In unpublished, preliminary studies, we have identified a new, phosphatase activity-independent role for Shp2 in control of a p53-dependent cell death pathway, a pathway that may help explain LS pathogenesis. PTPIB, in contrast, is typically a negative regulator of cell signaling. Surprisingly, however, we found that it is required for Neu-induced breast cancer. In the extension period, we will continue to use a combined genetic and - biochemical approach to understanding the detailed mechanism underlying NCFC syndromes and the role of PTPIB in breast carcinogenesis. We will complete generation of mouse models for other NS genes and for CFC. We will define the Shp2 phosphotyrosyl proteome and the new, activity-independent pathway controlling cell death. Finally, we will elucidate the detailed mechanism by which PITIB contributes to breast carcinogenesis, and assess whether these findings extend to human HER2+ breast cancer. Our results should be directly relevant to understanding the pathogenesis of human NCFC syndromes and cancer.